The present invention relates generally to optical systems, and more particularly, to optical single sideband millimeter wave generation for a super-broadband, optical wireless network.
Radio-over-fiber (ROF) techniques, the integration of optical and wireless systems, have become an attractive solution for increasing the capacity, bandwidth, and mobility to serve both fixed and mobile users. It also simplifies the configuration of the base station (BS) because the millimeter wave (mm-wave) signals will be generated and controlled in the central office (CO). Many optical mm-wave generation approaches have been reported, such as direct modulation, optical double-frequency heterodyning, external intensity modulation, and so on, but they have not been satisfactory. Direct modulation is limited by the laser chirp and the optical heterodyne technique is plagues by a lower frequency response and the quality of the mm-wave signals depends on the coherence of the two laser lightwaves in the optical heterodyning scheme. The external intensity modulation scheme can generate optical mm-wave signals with a simplified transmitter in the CO. Different modulation formats, such as double-sideband (DSB), single-sideband (SSB) and optical carrier suppression (OCS) can be generated by the external modulation scheme. However, due to fiber dispersion, DSB modulation experiences performance-fading problem and OCS modulation has the limitation of transmission distance, which shorter than 60 km if the 2.5 Gbit/s signal is carried by the 40 GHz optical carrier. To overcome fiber dispersion, the SSB modulation appears to be a viable option.
Accordingly, there is a need for a method of optical millimeter-wave generation using a single sideband modulation (SSB) that overcomes fiber dispersion and other limitations of previous techniques.